The term Prince of the Church is today used nearly exclusively for Catholiccardinals. However, the term is historically more important as a generic term for clergymen whose offices hold the secular rank and privilege of a prince (in the widest sense) or are considered its equivalent. In the case of Cardinals, they are always treated in protocol of Catholic countries as equivalents of royal princes.

By analogy with secular princes, in the broad sense of the ruler of any principality regardless of the style, it made perfect sense in a feudal class society to regard the highest members of the clergy, mainly prelates, as a privileged class ('estate') similar to the nobility, ranking just below or even above it in the social order; often high clerical ranks, such as bishops, were given high protocolary precedence amongst the nobility, and seats in the highest assemblies, including courts of justice and legislatures, such as Lord Bishops in the English (later British) House of Lords (where senior Anglican bishops and archbishops retain and use their rights to sit) and Prince primates in the Kingdom of Hungary.

In Europe, as it became common for younger sons of dynastic houses to seek careers in the church hierarchy, especially when they were expected to be excluded from the succession, members of royal families and the aristocracy began to occupy many of the highest prelatures; examples include Henry, Cardinal-Duke of York, the second grandson of James II of England, and Henry, Cardinal-King of Portugal, the fifth son of Manuel I of Portugal. Even popes openly created Cardinal nephews from their own family. However, these are individual cases; the term Prince of the church applies rather to the following institutionalised cases.

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Especially in the Holy Roman Empire, a large number of Prince-bishops, Prince-archbishops and superiors of the regular clergy (mainly Prince-abbots, but also -abbesses, Prince-Provosts and Grand masters) obtained for their seats, concurrent with the ecclesiastical office, one or more secular feudal estates of various status and importance (from tiny mere lordships to fairly great principalities such as duchies), that would otherwise be hereditary and often had been; in other cases territories were carved out especially by a higher authority, such as the empire, notably for an (arch)diocese or monastery, under such names as Stift (German; in the case of a diocese rather Hochstift, for an archdiocese rather Erzstift) or Sticht (Dutch), both meaning foundation, e.g. to set up a close relative as its first prelate; occasionally a normal secular style principality was created but immediately awarded to a prelate, such as the duchy of Westphalia for the Archbishop and Prince-elector of Cologne.

Many of them were at some point formally granted the rank of Reichsfürst, literally "Prince of the Empire", in itself entitling them to representation in the Reichstag (Imperial Diet). For example, the bishop of Liège was a Fürst on account of several secular principalities merged into the bishopric (including the countships of Loon/Looz and Ho(o)rn, marquisate of Franchimont and duchy of Bouillon) ruling a vast area, the prince-bishopric, but much smaller than his ecclesiastic diocese, the Bishopric of Liège in feudal times this territory was the only part of the Low Countries not counted among the "Seventeen Provinces" but seen as an integral part of the Holy Roman Empire. However the principalities of some of the highest prelates were not known as prince-(arch)bishopric, which they effectively were, but rather by a term corresponding to a more prestigious ecclesistial or temporal rank: the three German archbishoprics of Prince-electors (Mainz, Cologne and Trier) were styled Kurfürstentum 'Electorate'; the Patriarchate of Aquileia (an archbishopric of higher status) just that; the Bishop of Rome's - the Pope - Italian principalities the Papal State(s). On the other hand the papal principality in France, the Countship of Venaissin, where the papacy had resided in 'Babylonian exile' in Avignon, but which remained a papal state, separate from the Italian states, even after Avignon had been raised to archbishopric, was simply known by its temporal status, no reference to the highest of all princes of the Church.

An exclusively religious category of Princes were the Grand Masters, by somewhat different styles, of those military orders that had been granted statehood over a territory to defend it against the infidels and/or in recognition of the order's military merit in crusading and conquests, notably against the (mainly Slavonic and Baltic) peoples in the north and east —notably the State of the Teutonic Order became the major power in the Baltic region, for example, absorbing its counterparts— and against the MuslimMoors in Iberia. While the Grand masters and their fighting knights were usually professed nobles, the orders included clergy and were as a whole recognized as a truly "militant" form of devotion with papal recognition just as a normal monastic order. An existing example to this day would be that of the head of the Sovereign Military Order of Malta.

For analogous positions in non-Roman Catholic, and especially non-Christian contexts, the term Prince of the Faith is used.

In Hindu regions of the Indian subcontinent, the priestly caste of Brahmans ranks higher than the noble caste of Kshatriyas. As a result, princes of the faith can be considered the de jure superiors to princes of the blood. However, the two groups often competed with one another for de facto sovereignty, and some historic figures in Indian history have held both sacred and secular titles. As real power usually lay with the secular rulers, many Brahmins sought social promotion by serving them, e.g. as spiritual advisers at court, and even with (non-Hindu) occupying colonial powers, often in administrative positions where their intellectual qualities could be harnessed.